JPH0423570A - Gamma correction circuit - Google Patents

Abstract

PURPOSE:To realize the gamma correction circuit whose gamma correction characteristic is made variable with a smaller circuit scale than that of a conventional circuit by multiplying a coefficient K with a value read from a memory circuit so as to make the gamma correction characteristic variable. CONSTITUTION:A memory circuit 11 stores a difference between a level of a gamma correction characteristic curve and a level of a straight line Y=X by using a level of an input signal as an address. A multiplier circuit 12 multiplies a coefficient K with a value read from the memory 11 based on the level of the input signal and an adder circuit 13 adds an output of the multiplier circuit 12 and the input signal X to make the gamma correction characteristic variable. Thus, the gamma correction circuit whose gamma correction characteristic is made variable is realized with a smaller circuit scale than that of a conventional circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a gamma correction circuit, and particularly to a gamma correction circuit for digital video signals.

The present invention relates to a gamma correction circuit, and includes a storage means for storing a value on a curve obtained by subtracting a straight line Y=X from a gamma correction characteristic using the level of an input signal as an address; The gamma correction characteristic can be varied by having a multiplication means for multiplying a value read from the storage means based on the coefficient K by a coefficient K, and an addition means for adding the output of the multiplication means and the input signal. It is.

C0 Prior Art The relationship between the grid signal voltage and the light emission output of a color picture tube is not linear, and the light emission output is proportional to, for example, the 2.2 power of the input signal applied to the grid. For this reason, if a signal from a video camera is directly applied to a color picture tube, not only the brightness of the screen but also the hue and saturation will vary greatly. Therefore, before applying the input signal to the color picture tube, it is necessary to pass the input signal through a gamma correction circuit having an input/output characteristic such that the output signal is, for example, 1/2.2 power of the input signal to make the overall characteristic linear. is being carried out. This gamma correction circuit can be inserted just before applying the signal to the glycide of the color picture tube, but from the viewpoint of economy and stability, it does not belong to color picture receivers, which are household appliances. , is provided on the transmitting side, that is, the video camera.

In recent years, digital video signal processing technology for digitally processing video signals has become widely used in video cameras, and the gamma correction circuit is also constructed of digital circuits.

For example, by storing gamma correction characteristics in memory in advance,
A so-called mapping method is known in which a gamma-corrected digital video signal is read out from the memory. That is, the output signal level of the input/output characteristics of gamma correction is stored in memory in advance, the input signal level is used as a subsequent address in the memory, the output signal level is read from the memory, and this output signal is subjected to gamma correction. I am trying to set the signal to be the same.

Further, as shown in FIG. 7, for example, the gamma correction characteristic is approximated by a polygonal line, and as shown in FIG. 8, each of the straight lines of the polygonal line is The comparator circuit 51 realizes the characteristics of each arithmetic circuit 50 . A gamma correction circuit is known that compares the outputs of 5011 to 5011, selects the minimum value, and obtains a gamma-corrected digital video signal.

D1 Problems to be Solved by the Invention By the way, the mapping-based gamma correction described above requires a memory with a large capacity to store the values of all points on the curve (Y = X +1/-1) representing the gamma correction characteristics. becomes. Therefore, for example, when changing the gamma correction characteristics to match the gamma correction characteristics that differ for each broadcasting station, the entire memory must be rewritten, and because of the large capacity, it takes time to create data and write the created data to the memory. It was on.

In addition, in the gamma correction circuit having the configuration shown in FIG. 8 described above, if the number of straight lines is increased in order to increase the accuracy of the polygonal line approximation, the number of arithmetic circuits described above increases accordingly, resulting in an increase in the circuit scale. was there. Furthermore, it is difficult to realize this when the number of straight lines exceeds a certain value. In addition, in order to change the gamma correction characteristics, all arithmetic circuits 50. ~5
0. It was necessary to change the characteristics of l (coefficients a1, bi: i-1 to n), which was not practical.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gamma correction circuit capable of varying gamma correction characteristics with a circuit scale smaller than that of the conventional circuit.

Means for Solving the E0 Problem The gamma correction circuit according to the present invention includes a storage means for storing a value on a curve obtained by subtracting the straight line Y=X from the gamma correction characteristic using the level of a human input signal as an address, and a storage means for storing a value on a curve obtained by subtracting the straight line Y=X from the gamma correction characteristic, The above problem is solved by having a multiplication means that multiplies the value read from the storage means by a coefficient K based on the above, and an addition means that adds the output of the multiplication means and the input signal.

F0 action In the gamma correction circuit according to the present invention, the value read from the storage means is multiplied by a coefficient K to make the gamma correction characteristic variable.

G. Embodiments Hereinafter, embodiments of the gamma correction circuit according to the present invention will be described with reference to the drawings.

In FIG. 1, for example, a digital video signal X obtained by converting a video signal from a COD image sensor (hereinafter referred to as CCD) of a video camera into a digital signal is supplied to a memory circuit 11 and an adder circuit 13 via an input terminal 1. .

The memory circuit 11 is, for example, a random access memory (
As shown in FIG. 2, the memory circuit 11 has a gamma correction characteristic, that is, y
The value on the curve obtained by drawing a straight line represented by Y=X from the curve represented by =
) is stored with the above-mentioned human-powered digital video signal X as a successive address, as shown by the solid line curve in FIG. The reference data Δy stored in the memory circuit 11 is read out based on the input digital video signal X, and the read reference data Δy is supplied to the multiplication circuit 12.

The multiplication circuit 12 multiplies the coefficient K supplied via the terminal 3 for changing the gamma correction characteristic, and supplies the multiplication result to the addition circuit 13 .

The adder circuit 13 adds the output of the multiplier circuit 12 and the human-powered digital video signal X, and sends the addition result to the output terminal 2 as a gamma-corrected digital video signal Y.
Output from.

Thus, in this embodiment, the memory circuit 11 is used as a storage means for storing the value on the curve obtained by subtracting the straight line Y=X from the gamma correction characteristic, using the level of the input signal as an address, and the multiplier circuit 12 The adder circuit 13 is used as a multiplier for multiplying the value read out from the memory 11 by a coefficient K based on the level of the multiplier 1.
It is used as an adding means to add the output of 2 and the input signal.

Next, the operating principle of the gamma correction circuit having the above-described configuration will be explained.

The reference data Δy read from the memory circuit 11 is zero at the points where the input digital video signal X is 0% and 100%. Therefore, by changing the coefficient K supplied through the terminal 3, the output of the multiplier circuit 12 can be changed to the input digital video signal X, as shown by the broken line in FIG.
does not change at 0% and 100% points, and becomes twice the reference data Δy at other points. Therefore, in the gamma correction circuit of this embodiment, as shown in FIG. 4, the curve of the gamma correction characteristic is changed without changing the gamma correction characteristic at the points where the input digital video signal X is 0% and 100%. You will be able to do that.

As described above, in the gamma correction circuit of this embodiment, the value on the curve obtained by subtracting the straight line Y=X from the gamma correction characteristic, that is, the reference data Δy, is stored in the memory circuit 11.
By multiplying the reference data Δy read from the memory circuit 11 based on the human-powered digital video signal X by a coefficient K in the multiplication circuit 12, and adding the output of the multiplication circuit 12 and the input digital video signal X in the addition circuit 12,
Gamma correction characteristics can be made variable. Further, the arithmetic circuit can be configured with one multiplier circuit 12 and one adder circuit 13, and a gamma correction circuit that can vary gamma correction characteristics can be configured with a smaller circuit scale than in the past.

Next, another embodiment of the gamma correction circuit according to the present invention will be described.

In the embodiment shown in FIG. 1, the memory circuit 11 stores the values of all points on the curve (reference data Δy) obtained by subtracting the straight line Y-x from the gamma correction characteristic.
A memory with a certain amount of capacity was required. Therefore,
A curve obtained by drawing a straight line Y=X from the gamma correction characteristic is approximated by a polygonal line, and data on the slope and bending point of each line segment is stored. Specifically, the configuration is as follows.

As shown in FIG. 5, the input digital video signal
is supplied to

The encoder 21 converts the human-powered digital video signal X into successive addresses of the memory circuit 22.

The memory circuit 22 is composed of, for example, a RAM, and the memory circuit 22 has a gamma correction characteristic, that is, y ==
Draw a straight line represented by Y=X from the curve represented by The level of the input digital video signal X (hereinafter referred to as bending point data X1) and the level of the broken line in this bending point data xlI (hereinafter referred to as intercept data b) are stored.

Slope data aff stored in this memory circuit 22
i, intercept data b, and bending point data X are read out based on successive addresses from the encoder 21, and this read bending point data Xm is supplied to the subtraction terminal of the adding circuit 23, Slope data a0 is supplied to a multiplication circuit 24, and intercept data b is supplied to an addition circuit 25.

The adder circuit 23 converts the input digital video signal X supplied via the input terminal 4 into the bending point data X,
is subtracted, and the subtraction result is supplied to the multiplication circuit 24.

The multiplier circuit 24 multiplies the output of the adder circuit 23 by the slope data a1 from the memory circuit 22, and supplies this multiplication result to the -1 adder circuit 25.

The adder circuit 25 adds the output of the multiplier circuit 24 and the intercept data b from the memory circuit 22, and supplies the addition result to the multiplier circuit 26.

The multiplication circuit 26 multiplies the output of the addition circuit 25 by a coefficient K for changing the gamma correction characteristic supplied via the terminal 5, and supplies the multiplication result to the addition circuit 27.

The adder circuit 27 adds the output of the multiplier circuit 26 and the human digital video signals M and X, and outputs the addition result from the output terminal 6 as a gamma-corrected digital video signal Z.

Thus, in this embodiment, the straight line Y is determined from the gamma correction characteristics.
A storage means for storing the value of the curve obtained by subtracting ``2'' by using the level of the input signal as an address is comprised of the encoder 21 to the addition circuit 25, and a multiplication circuit 26 stores the value of ``2'' based on the level of the input signal. The adder circuit 27 is used as an adder to add the output of the multiplier circuit 26 and the input signal.

Next, the operation of the gamma correction circuit having the above-described configuration will be explained.

As described above, the memory circuit 22 draws a straight line represented by Y=X from the gamma correction characteristic, approximates the obtained curve to a polygonal line, and stores slope data aLI of each line segment of this polygonal line and each bending point. Bending point data X1, which is the level of the human-powered digital video signal, and intercept data b+ at the bending point data X are stored. Specifically, a curve obtained by drawing a straight line represented by Y=X from the gamma correction characteristic is drawn, for example, as shown in FIG.
When is less than 0% of the reference white level,
When the change in the output signal is in a large black area from 0% to 15%, it is approximated by 16 polygonal lines, and when it is from 15% to 120%, it is approximated by 1
4 Approximate with a polygonal line, and when it is 120% or more, approximate with a polygonal line. Then, the slope data a of each line segment of these 32 polygonal lines is set to 8 bits, and the bending point data Xff1 is set to 14 bits.
As bits, intercept data bff at each level X1
i is divided into 11 bits and stored in the memory circuit 22.

The encoder 21 converts the input digital video signal χ into a subsequent address of the memory circuit 22. Specifically, in the case of the above-mentioned 32-line approximation, when the input digital video signal
%~15%, convert to 16 addresses, 15%
~120%, convert to 14 addresses, 120
% or more, convert to one address. However, it is converted into a 5-hit successive address corresponding to the 32-line approximation. Then, the bending point data X read out using this successive address is supplied to the adder circuit 23, the slope data a0 is supplied to the multiplier circuit 24, and the intercept data b,
is supplied to the adder circuit 25.

Then, the addition circuit 23 subtracts the bending point data X1 from the input digital video signal b, the multiplier circuit 26 multiplies the output of the adder circuit 25 by the coefficient K supplied via the terminal 5, and the adder circuit 27 adds the output of the multiplier circuit 26 and the input digital video signal X. ,
A gamma-corrected digital video signal Z, z−(aLIx(X=X11)+b,)XK+X ・・ is output from the output terminal 6.
-(1) is output.

By the way, the input digital video signal X is 0% and 10%.
At the 0% point, the value of the first term in equation (1) above is zero.

Therefore, in the gamma correction circuit of this embodiment, the coefficient K
By changing the input digital video signal
This means that the curve of the gamma correction characteristic can be changed without changing the gamma correction characteristic at the points of 0% and 100%.

As described below, in the gamma correction circuit of this embodiment, the curve obtained by drawing a straight line represented by Y=X from the gamma correction characteristic is approximated by a polygonal line, and the slope data ap and the intercept data b□ of each line segment are approximated. , bending point data X.

is stored in the memory circuit 22 in advance. Then, the encoder 21 converts the input digital video signal X into successive addresses of the memory circuit 22, and receives slope data a from the memory circuit 22 based on the successive addresses. , intercept data b
B. A digital video signal Z whose gamma correction characteristics are made variable by reading the bending point data can be obtained. In this case, the memory circuit 22 does not need to store data for each point on the polygonal line; for example, in the case of 32 polygonal line approximation as described above, 32 sets of slope data a1, intercept data b0, and bending point data , so the memory circuit 22
capacity can be reduced. In addition, the arithmetic circuit is also 2
one multiplier circuit 24.26 and three adder circuits 23.25.
27, it is possible to construct a gamma correction circuit that can vary gamma correction characteristics with a circuit scale smaller than that of the conventional circuit.

H9 Effects of the Invention As is clear from the above explanation, in the gamma correction circuit according to the present invention, the straight line Y=
The second value of the curve obtained by subtracting X is stored using the level of the input signal as an address, the multiplication means multiplies the value read from the storage means based on the level of the input signal by a coefficient K, and the addition means multiplies the value read from the storage means based on the level of the input signal. By adding the output and the input signal, the gamma correction characteristics can be made variable. Further, the storage means only needs to store one reference gamma correction characteristic, the capacity of the storage means can be reduced, and the circuit for the above calculation can be easily configured.
It is possible to realize a gamma correction circuit that can vary gamma correction characteristics with a smaller circuit scale than conventional ones. In other words, the gamma correction circuit can be easily integrated into an IC, and the power consumption can be reduced compared to the conventional method. Furthermore, for example, by changing the coefficient K, it is possible to easily cope with gamma correction characteristics that vary depending on the broadcasting station.

Further, by applying a polygonal approximation to the curve obtained by drawing the straight line Y=X from the gamma correction characteristic, the memory capacity can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a gamma correction circuit according to the present invention, FIG. 2 is a diagram showing gamma correction characteristics for explaining the invention in detail, and FIG. 3 is a diagram showing gamma correction characteristics. FIG. 4 is a diagram showing the gamma correction characteristic when the coefficient K is made variable, and FIG. 5 is a block diagram showing another embodiment. 6 is a diagram showing a polygonal line when the curve obtained by subtracting the straight line Y=X from the gamma correction characteristic is approximated by a polygonal line, and FIG. FIG. 8 is a diagram showing a polygonal line when approximated;
The figure is a block diagram of a conventional gamma correction circuit. Memory circuit Multiplying circuit Adding circuit Encoder Memory circuit Multiplying circuit 27 Adding circuit 11 12 13 21 22 24, 26 23, 25,

Claims (1)

[Scope of Claims] Storage means for storing a value on a curve obtained by subtracting the straight line Y=X from the gamma correction characteristic using the level of an input signal as an address; A gamma correction circuit comprising a multiplication means for multiplying a value by a coefficient K, and an addition means for adding an output of the multiplication means and an input signal.